Air pollution has become a major problem in recent years and there is currently much time, effort and expense being put forth to devise economical schemes for reducing this pollution. One of the many sources of air pollution is the flue gases emitted from fuel-burning equipment such as steam generating units. The sulfur oxides, SO.sub.2 and SO.sub.3, are of major concern as air pollutants in such flue gases. The particulate matter such as fly ash and other dust particles also contribute to the pollution problem if not completely removed. Most of the schemes which have been developed to date to remove these obnoxious flue gas constituents have involved either or both high capital investment and high operating cost rendering the schemes impractical.
One approach to this air pollution control problem has been to remove SO.sub.2 and SO.sub.3 by reaction with carbonates primarily calcium and/or magnesium carbonate in the form of limestone or dolomite. These are cheap, readily available materials, but problems arise in effecting a complete reaction and removal of all the sulfur oxides. One such process is referred to as the dry limestone process and involves the addition of dry pulverized limestone directly to the furnace. The carbonate is calcined to the oxide form which reacts with the sulfur oxides. Although there is almost complete reaction of SO.sub.3 with the additive, most of the sulfur is in the dioxide form and reaction of the sulfur dioxide might be only on the order of 50 percent or less. This is an unsatisfactory ultimate solution to the pollution problem.
Another approach is an extension of the above-described dry limestone process and incorporates a wet scrubber. This wet scrubber, in addition to removing particulate matter, acts as a reactor in which the calcium and/or magnesium oxides dissolve in the scrubber water and react in the liquid phase with the SO.sub.2. Since there is a relatively short residence time of the gases and additive in the scrubber water, getting the additive dissolved and reacted can be a problem without very careful scrubber design. Also, pH control of the scrubber water can be difficult which can cause problems such as scaling and corrosion.